Method and apparatus for non-invasive blood glucose sensing

ABSTRACT

A method and apparatus (12) for the non-invasive sensing of blood glucose levels includes apparatus (10) which moves the forearm of the patient in a controlled incremental manner to take a plurality of spectral skin measurements and averaging the measurements for the purpose of accounting for biological differences that exist in the patient&#39;s skin.

This application claims benefit of Provisional Application Ser. No.60/012,305, filed Feb. 23, 1996.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical diagnostic methodsand apparatus and, more particularly, to methods and apparatus for thenon-invasive sensing of blood glucose levels.

2. Description of the Prior Art

In the treatment of diabetes, it is oftentimes necessary for theafflicted patient to periodically monitor his or her blood glucose leveland then administer appropriate amounts of insulin in response to theglucose level so determined. Heretofore, it has been common to employ apin prick to the finger in order to draw a blood specimen to determinethe glucose level. More recently, non-invasive tests have been developedfor this purpose.

It is generally known in the art that radiation, particularlynear-infrared radiation over a range of wavelengths, can be projected ina non-invasive manner on a portion of the body of a patient. Theresulting radiation emitted from that portion of the body, eitherscattered or transmitted after absorption and scattering, can bedetected and processed to derive an expression of the detected radiationas a function of wavelength and, therefrom, the concentration of bloodglucose. Since the detected radiation is a continuous signal coveringall of the wavelengths in the range of interest, it is necessary forfurther analysis to separate the intensities of radiation at the variousindividual wavelengths, or smaller bands of wavelengths, to extract thedesired blood glucose level information.

U.S. Pat. Nos. 5,070,874 and 5,460,177 describe methods for thenon-invasive measurement of blood glucose levels. In general, thesemethods use a spectrophotometer to measure the absorbency of thenear-infrared radiation at different wavelengths across the range ofinterest. The absorbency plotted against the wavelengths constitutes aspectrum. By analyzing the spectrum, the blood glucose levels, orchanges thereto, can be determined. As the blood glucose levels vary,the detected spectrum changes slightly.

In order to make the measurements discussed above, the radiation must betransmitted from a radiation source via a sensor head to the skin of apatient and the detected radiation received back from the skin must becollected at the sensor head and carried to a spectrophotometer forfurther analysis. When making such fine spectral skin measurements, thesensor system measures only a small area of skin which is in intimatecontact with the sensor head. Human skin consists of biologicalcomponents that may be different from point to point over a given area.There may be, for example, certain types of skin cells or hair folliclesthat vary in composition over a given area of skin. Accordingly, asingle, non-invasive measurement of blood glucose level within a givenarea will vary as greatly as the skin composition itself.

It is an object of the present invention to account for the naturallyoccurring biological skin variations of a patient so as to permitnon-invasive glucose measurement of greatly enhanced reliability andaccuracy. It is a further object to provide an apparatus and methodwhich permits self testing by the diabetes patient without the need forspecialized clinical assistance.

SUMMARY OF THE INVENTION

Briefly stated, an apparatus according to the invention includes ahousing frame for mounting conventional electronic means including aspectrophotometer, electronic control logic and associated hardware forgenerating and measuring blood glucose by near-infrared radiation. Theimproved apparatus comprises an arm tray slidably mounted on the housingframe. The arm tray is configured to receive a patient's forearm in aresting mode thereon and position an area of the forearm over a sensorhead which is operably coupled to the electronic means of the apparatus.The arm tray is mounted on linear bearings to permit movement of thetray along with the patient's resting forearm in a linear directionalong a horizontally extending, longitudinal axis of the patient'sforearm. The sensor head is preferably fixed relative to thelongitudinal axis of the forearm and extends upwardly through anelongated opening in the arm tray to directly contact the patient's skinwhen blood glucose sensing measurements are made. A stepper motorrotatably actuates a reciprocating lead screw causing selective linearmovement of the arm tray which, in turn, provides controlled movement ofthe patient's skin relative to the sensor head. One or more bloodglucose measurements are made at selected spaced-apart locations alongthe patient's forearm when the arm tray has stopped. The plurality ofmeasurements is then averaged to obtain a representative blood glucosereading which accurately accounts for biological skin variationsoccurring over the scanned area.

A further embodiment of the apparatus and method of the inventionincludes mechanical means for lifting the patient's skin away fromcontact with the sensor head after a blood glucose measurement is madeand movement of the arm tray commences. The skin lifting means comprisesa roller mechanism surrounding the sensor head. A linkage and strutassembly carries the roller mechanism and is vertically moveable by asolenoid cylinder. When the solenoid is selectively actuated, at thetime when the arm tray is to begin movement, the roller mechanism israised by the linkage and strut assembly to push the rollers to directlycontact and press against the patient's arm. The vertical movement ofthe roller mechanism is controlled so that the surface of the patient'sskin is moved only a small distance from the sensor head surface. Theroller mechanism then permits the skin to slide and roll over aspaced-apart pair of rollers as the arm tray moves to reposition thepatient's arm at a new skin site for a next blood glucose measurement.Once positioned at the new site, the solenoid is automaticallydeactivated to lower the linkage assembly and roller mechanism. In thismanner, as the roller mechanism drops below the level of the sensorhead, the patient's forearm skin is again brought into contact with thesensor head, accurately positioned for the next blood glucosemeasurement.

These, as well as other attributes and advantages of the presentinvention, will become more apparent when reference is made to thedrawings taken with the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a non-invasive blood glucose monitorhaving a moveable arm tray according to the invention;

FIG. 2 is a perspective view of the arm tray subassembly of the bloodglucose sensor of FIG. 1;

FIG. 3 is a perspective view of the mounting and drive system for themoveable arm tray of FIG. 2; and

FIG. 4 is a perspective view of a roller and skin lifting mechanismaccording to the invention for use in the blood glucose sensor of FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A non-invasive blood glucose monitor 2 embodying features of the presentinvention is depicted in FIG. 1. The blood glucose monitor 2 is anoninvasive diagnostic device which permits a diabetes patient toperform self-monitoring blood glucose measurements so as to maintainproper insulin levels. The monitor 2 includes a screen 4 for displayingblood glucose levels and related information and further includes pushbutton controls 6, or the like, for activation and deactivation of themonitor by the patient. The monitor 2 further includes a sensor head 8which is intended to make contact with the skin of a patient's forearmsituated on the moveable arm tray 10.

The monitor 2 includes an enclosing housing 9 and an underlying supportframe 12 for mounting the various electronic means therein, including aspectrophotometer and appropriate electronic control logic and otherconventional assorted hardware for generating a near infrared radiationbeam at appropriate times and durations. Also included are means forsensing and measuring blood glucose levels based on the amount ofradiation sensed. The radiation is transmitted from the sensor head tothe underside forearm skin of a patient and the radiation emitted fromthe patient is transmitted to the spectrophotometer for analysis, all ofwhich is well-known in the art. The present invention concerns themethod and apparatus for overcoming biological skin variations whichcause significant variations in blood glucose measurements when finespectral measurements are required.

In order to accomplish this desired objective, the present inventionincludes a moveable arm tray 10, the details of which are more readilyunderstood with reference to FIGS. 2 and 3. The arm tray 10 is slidablein a horizontal plane relative to the fixed frame 12 of the glucosemonitor 2. The arm tray is slidably attached to a plurality of linearbearings 14, one of which is shown in FIG. 3, which travel on fixedbearing shafts 16 carried by the fixed housing frame 12. Preferably,three bearings 14 and shafts 16 are employed. A stepper motor 20 ismounted on the fixed housing frame 12 and carries a reciprocating leadscrew 22 which moves inwardly or outwardly when the motor is rotated inone of two directions. The lead screw engages a fixed bracket 24 mountedon the arm tray 10 which then will cause controlled movement of the armtray when the stepper motor is actuated. Through selection of anappropriate stepper motor and thread pitch of the lead screw, it ispossible to control movement of the arm tray 10 in increments as fine as0.01". Total travel distance of the arm tray along the shaft bearing 16is preferably between about 31/2 to 4".

The arm tray 10 also preferably includes a padded elbow portion 26 and apadded handrest portion 28. The end 30 of the handrest portion serves asa guide or gripping point for the fingers of the patient and functionsto position the underside of the patient's forearm over the sensor head8. The padded portions 26 and 28 are moveable within the grooved guides26' and 28', respectively, to permit length adjustment to accommodateforearms of various lengths.

The arm tray 10 further includes a cutout portion 11 in a central regionthereof to permit the sensor head 8 to directly contact the skin of thepatient's forearm. Appropriate control means and logic located in theelectronics package of the monitor 2 cause periodic activation of thestepper motor 20 to cause movement of the arm tray relative to thesensor head 8 in a controlled incremental manner so that individualblood glucose measurements can be made in a predetermined array ofrepeated short and long increments along a longitudinal axis of thepatient's forearm, for example, along a total length of 31/2". Themeasurements are then averaged to obtain an accurate glucose measurementwhich takes into account the variations in the biological components ofthe skin which may differ from point-to-point over the given measurementfield. The movement of the arm tray is adjustable so that the armmovement pattern relative to the sensor head is adjustable and can thusbe optimized for each patient.

The arm tray 10 is configured to receive a patient's forearm in aresting mode thereon to position the underside or hairless area of thepatient's forearm over the sensor head 8. As previously stated, thesensor head 8 is operably coupled to the electronic means of theapparatus. The arm tray 10 is mounted on the linear bearings 14 topermit smooth and accurate movement of the patient's resting forearmover the sensor head 8 along the longitudinal axis of the forearm. Thesensor head 8 is fixed relative to the longitudinal axis of the forearmand extends upwardly through the opening 11 in the tray to directlycontact the patient's skin when glucose sensing measurements are made.Activation of the stepper motor activates the lead screw to selectivelycause controlled linear movement of the arm tray 10 over an area of thepatient's skin to be monitored.

The present invention preferably includes a lifting means for moving thepatient's skin out of contact with the sensor head as the arm tray ismoved. The lifting mechanism is depicted in FIGS. 3 and 4 in greaterdetail and identified generally by reference numeral 40. The skinlifting mechanism 40 includes a roller assembly comprising twospaced-apart rolls 44 which are rotatable about shafts 46 carried by asupport frame 48. The rollers 44 may be, for example, 0.180" indiameter. The roller surfaces make up most of the surface that comes incontact with the patient's skin. However, a small portion of the rollersupport frame 48 may come in contact with the patient's skin duringoperation. Hence, the materials of construction are preferably inert andimpervious to body acids as well as cleaning solvents used duringmaintenance of the apparatus. The roller and frame materials preferablyemploy acetyl plastic as a preferred material of construction. Thismaterial provides both inert and non-stick characteristics and providesa good bearing material to accommodate rotation of the rollers 44.

The roller support frame 48 is carried by a linkage system including apair of struts 50. The struts 50 of the linkage system are pivotallyattached at their ends 50' to a stationary yoke 52. A vertical member 54is attached to the pivoting ends 50' of the struts 50 to move therewith.The lower end 56 of the vertical linkage member 54 is attached to an endof a solenoid shaft 58 which is selectively moved by a solenoid 60. Asseen in FIG. 4, inward movement of the solenoid shaft 58 causes themoving portions of the vertical member 54 and the struts 50 of thelinkage system to pivot about axis 42. Inward movement of the solenoidshaft 58 thus causes the strut arms 50 to raise the roller support frame48 and rollers 44 above the level of the sensor head 8. As stated above,the sensor head 8 is fixedly mounted relative to the housing frame 12.

At a time when the arm tray 10 is to begin movement, the solenoid 60 isactivated. The roller mechanism 40 is then moved upwardly, as describedabove, causing the rollers 44 to raise and engage the patient's arm. Thevertical movement of the rollers 44 is controlled so as to separate thesurface of the patient's skin a small distance from the surface of thesensor head 8. The lifting mechanism then permits the skin to slide androll over the spaced-apart rollers 44 out of contact with the sensorhead as the arm tray 10 moves to reposition the patient's arm to a newskin site for a next measurement. Once positioned at the new location,the solenoid 60 is deactivated to cause an extension of the shaft 58,causing reverse pivotal movement of the skin-lifting mechanism 40 aboutpivot axis 42 to lower the rollers 44. In this manner, as the rollers 44drop below the level of the sensor head 8, the patient's forearm skin isagain placed in contact with the sensor head 8, thus accuratelypositioning the sensor head for a next measurement.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. For example, while theabove-described, presently preferred embodiment of the invention causesthe forearm to move relative to a fixed sensor head, of course, theforearm could remain fixed and the sensor head could be moved or, stillfurther, both the sensor head and the forearm could be moved in acontrolled manner. Accordingly, the presently preferred embodimentsdescribed herein are meant to be illustrative only and not limiting asto the scope of the invention which is to be given the full breadth ofthe appended claims and any and all equivalents thereof.

What is claimed is:
 1. Apparatus for monitoring blood glucose levels ina patient, said apparatus of the non-invasive, near infrared typeincluding a monitor housing having means for generating and measuringnear infrared radiation, wherein the improvement comprises:a) a sensorhead operably coupled to the near infrared radiation generating andmeasuring means for directing and receiving said radiation to and from apatient's skin; b) an arm tray slidably mounted on said monitor housingadjacent to said sensor head for supporting a forearm of the patientthereon and to position the forearm relative to the sensor head; and c)motive means for incrementally moving and stopping the arm tray relativeto the sensor head over a selected distance to permit a plurality ofblood glucose measurements to be made along a given area of forearm skinof the patient.
 2. The apparatus of claim 1 including means for liftingthe skin of the patient away from the sensor head when the arm tray isselectively moved and for returning the skin to a position in contactwith the sensor head means when the arm tray is stopped.
 3. Theapparatus of claim 2 wherein the skin lifting means includes a pair ofspaced-apart rollers positioned on opposed sides of the sensor head,said rollers mounted for rotation on a roller support frame, linkagemeans connected to said roller support frame for raising said rollers toa position above a sensing surface of the sensor head and for loweringsaid rollers to a position below said sensing surface; and motive meansfor moving the linkage means to selectively raise and lower the rollers.4. The apparatus of claim 3 wherein the arm tray has an opening thereinto permit the sensor head and skin lifting means to directly contact anunderside skin surface of the patient's forearm at selected intervals.5. The apparatus of claim 1 including hand grip means positioned at anend of the arm tray for grasping by the patient to locate the patient'sforearm relative to the sensor head.
 6. A method of monitoring a bloodglucose level by use of near infrared radiation in a patient comprisingthe steps of:a) positioning a sensor head of a blood glucose monitor ata first skin site of the patient; b) performing at least one bloodglucose measurement at said first skin site; c) repositioning the sensorhead to a next skin site and, at the same time, lifting the skin of thepatient away from the sensor head; d) performing at least one bloodglucose measurement at said next skin site; e) repeating steps c) and d)a plurality of times to conduct blood glucose measurements over a givenarea of skin; f) averaging the blood glucose measurements made in stepsb)-e); and g) releasing the skin to contact the sensor head during stepsb) and d).
 7. The method of claim 6 wherein the positioning andrepositioning steps comprise selective movement of a forearm of thepatient relative to the sensor head.
 8. The method of claim 6 whereinthe skin sites are located on a patient's forearm.